1. Field of the Invention
The present invention relates to an exposure apparatus, which is used in a lithography process to manufacture devices.
2. Description of the Related Art
A projection exposure apparatus has been conventionally used as an apparatus that projects a circuit pattern image drawn on a reticle, serving as an original, onto a wafer, a glass plate, or the like, serving as a photosensitive substrate, by a projection optical system, and exposes the photosensitive substrate.
In recent years, an immersion exposure apparatus has attracted attention, in which a liquid is present between a projection optical system and a photosensitive substrate, and the refractive index of a medium between the final surface of the projection optical system and the photosensitive substrate is increased to achieve a high resolution. In this immersion exposure apparatus, the liquid fills the gap between the projection optical system and the photosensitive substrate (to be merely referred to as a “substrate” as well hereafter), to increase the numerical aperture (NA) of the projection optical system. The numerical aperture (NA) of the projection optical system can be obtained from NA=n·sin θ where n is the refractive index of the liquid (medium). Thus, the NA can increase to n by filling the gap with a medium having a refractive index higher than that of air (n>1). From this relationship, a resolution R (R=k1(λ/NA)) of the immersion exposure apparatus, which is represented by a process constant k1 and a wavelength λ of the light source, can be decreased.
For example, a so-called local fill scheme immersion exposure apparatus has been proposed in which a liquid locally fills the gap between the final surface of a projection optical system and the surface of a wafer. The local fill scheme immersion exposure apparatus requires a specific mechanism, when exposing the peripheral portion of the wafer, to hold the liquid locally between the final surface of the projection optical system and the surface of the wafer. Japanese Patent Laid-Open Nos. 2004-289127, 2002-158154, 2005-101488, and 2005-72132 propose an immersion exposure apparatus, which has a liquid holding plate (auxiliary member), adjacent to the peripheral portion of a wafer and having almost the same height as that of the surface of the wafer, on the stage top plate.
Japanese Patent Laid-Open No. 2005-101488 discloses an arrangement in which a recovery hold member or a porous member is arranged on a wafer stage, and connects to a line which is pressure-reduced by a vacuum pump, or the like, to recover an immersion liquid, entering a groove in the peripheral portion of the substrate, by suction.
With the liquid holding plate having almost the same height as that of the wafer on the stage top plate, when scanning the wafer, part of a liquid membrane (LW) locally held between the final surface of the projection optical system and the wafer surface remains thin on the surface of the liquid holding plate. When the thin liquid membrane remaining on the surface of the liquid holding plate vaporizes, it decreases the temperature of the liquid holding plate. The temperature decrease thermally deforms (shrinks) the liquid holding plate to deform a top plate that supports the liquid holding plate. When the top plate deforms, the relative positional relationship between the measurement mirror of a laser interferometer arranged in the vicinity of the top plate and the wafer changes, to degrade the measurement accuracy of the position and the posture of the wafer.
To recover the remaining immersion liquid, if the wafer stage is provided with a recovery hole member or a porous member to recover the immersion liquid by negative pressure suction, suction decreases the atmospheric pressure near the immersion liquid to promote vaporization of a significant amount of the immersion liquid. In other words, when the quantity to vaporize changes depending on the relative relationship between the pressure around the immersion liquid and the vapor pressure of the immersion liquid, and the pressure around the immersion liquid changes in a decreasing direction, usually, the vaporization quantity increases. Accordingly, the portion around the flow channel, including the recovery hole member or porous members as the suction portion and the vacuum pump, tends to be cooled due to the influence of the vaporization heat. It is known that (pure) water typically used as an immersion liquid, particularly, has a very large heat quantity of vaporization (latent heat) per unit mass, and that vaporization of 1 g of water deprives the flow channel of as large as about 2,400 J of heat. The heat vaporization generated by the immersion liquid deprives a member surface of a vary large heat quantity, directly and locally. Hence, it is difficult to perform highly accurate temperature adjustment, including temperature distribution adjustment, of the entire liquid holding plate. Therefore, in practice, even with temperature adjusting, thermal deformation occurs to a certain degree, due to a change in temperature of the wafer liquid holding plate, to degrade the exposure accuracy.
The present invention has been made in view of the above problems, and has as its object to provide an exposure technique which suppresses an influence of the thermal deformation of the liquid holding plate caused by vaporization heat of an immersion liquid, and realizes excellent exposure accuracy.